Geometry-assisted dielectrophoretic localization on a CMOS sensor array for label-free detection of viable Escherichia coli.

Rapid and sensitive detection of viable bacteria is essential in food safety, healthcare, and environmental monitoring. Although label-free electrical biosensing offers a rapid and simplified alternative to conventional methods, its performance is often constrained by inefficient transport and accumulation of target cells at the sensing interface. Here, we present a microfluidic geometry-assisted dielectrophoretic (DEP) enrichment strategy integrated with a 65 GHz LC-oscillator dielectric sensing platform for label-free detection of Escherichia coli. A Y-shaped microfluidic architecture coupled with a high-density DEP electrode array (62 × 24, 3 × 3 mm2) enables spatial redistribution of bacteria from a wide upstream region into a confined downstream detection channel. This geometry-induced concentration enhances the effective local cell density per sensing element, thereby amplifying the initial sensing response under the same DEP operating conditions. Under optimized conditions (500 kHz, 0.01 S m-1), distinct DEP behaviors of live, pasteurized, and autoclaved cells enable preferential enrichment of viable bacteria. Compared with a straight-channel configuration, the proposed design achieves a 20-fold enhancement in sensitivity, with a detection limit of 4.4 × 103 CFU mL-1 within 20 min, further improved to 8.8 × 102 CFU mL-1 with extended enrichment. Unlike systems that use the same electrodes for DEP manipulation and impedance sensing, this platform separates the two electrical functions into co-located DEP and LC sensing units. It enables localized, per-element frequency-shift mapping of geometry-enhanced bacterial accumulation within the CMOS array.